When a module containing


module nxt.rational;

Rational!(I1) rational(I1, I2)(I1 , I2)
{
    return typeof(return)();
}

struct Rational(Int)
{
    bool opEquals(Rhs)(Rhs _) {}
}

@nogc unittest
{
    auto _ = rational(1, 2);
}


is used as the sole module of a dub project then `dub test` fails as

.dub/build/phobos-next-test-library-unittest-linux.posix-x86_64-dmd_2092-06C9DAF60B64114484B3FE9AC9866D5F/phobos-next-test-library.o:src/nxt/rational.d:_D40TypeInfo_S3nxt8rational__T8RationalTiZQm6__initZ: error: undefined reference to '_D6object10_xopEqualsFMxPvMxQeZb'

When I remove

    bool opEquals(Rhs)(Rhs _) {}

the error goes away.

I'm suspecting this is a bug in dmd that fails to correctly check if a struct has its templated `opEquals` instantiated.

For a complete minimal sample project see

https://github.com/nordlow/phobos-next/tree/master/rational.reduced

On Sunday, 21 June 2020 at 12:42:11 UTC, Per Nordlöw wrote:
> When a module containing

BTW this fails for dmd stable and dmd nightly but works for ldc 1.22.0.

On Sunday, 21 June 2020 at 12:42:11 UTC, Per Nordlöw wrote:
> I'm suspecting this is a bug in dmd that fails to correctly check if a struct has its templated `opEquals` instantiated.

I'd suggest taking dub out of the equation then, so that you can file a DMD issue once you can confirm it. Your sample works with `-main -unittest` on run.dlang.io, so it seems to depend on how the test executable is built.

On Sunday, 21 June 2020 at 16:58:43 UTC, kinke wrote:
> Your sample works with `-main -unittest` on run.dlang.io

After quickly looking at your list of compiler flags in dub.sdl, the problem manifests when adding `-preview=in`. Please file an issue.

On Sunday, 21 June 2020 at 17:05:11 UTC, kinke wrote:
> On Sunday, 21 June 2020 at 16:58:43 UTC, kinke wrote:
>> Your sample works with `-main -unittest` on run.dlang.io
>
> After quickly looking at your list of compiler flags in dub.sdl, the problem manifests when adding `-preview=in`. Please file an issue.

Thanks a lot! I'll do so.

On Sunday, 21 June 2020 at 17:05:11 UTC, kinke wrote:
> Please file an issue.

Done: https://issues.dlang.org/show_bug.cgi?id=20968

On Sunday, 21 June 2020 at 22:48:20 UTC, Per Nordlöw wrote:
> On Sunday, 21 June 2020 at 17:05:11 UTC, kinke wrote:
>> Please file an issue.
>
> Done: https://issues.dlang.org/show_bug.cgi?id=20968

You can get more info compiling with "-verrors=spec"

"(spec:1) Error: template rational.Rational!int.Rational.opEquals cannot deduce function from argument types !()(const(Rational!int)) const, candidates are:"

From reading the docs for function opEquals (https://dlang.org/spec/operatoroverloading.html#equals).
It shows a templated version with a const modifier.
If you change the function signature to:

bool opEquals(Rhs)(Rhs _) const {return true;} // Note the 'const', and putting some return back because dustmite removed it

The program links fine.

So it seems a compiler error is gagged that should be exposed and also could be improved.